A Highly Integrated, 2-Channel IFB System for
Mobile Applications
The IFB Plus Series is designed for electronic news-gathering (ENG) trucks, satellite news-gathering
(SNG) trucks, and small production vehicles. Interruptible foldback (also known as talent cueing)
allows reporters and other on-air talent to receive program audio along with audio cues from production personnel, generally directors and producers. The design and implementation of a studio IFB system can be quite
complex, yet normally remains the same from day to day. Talent and production personnel, along with the IFB
equipment, are physically located in the same facility.
Mobile IFB applications can present increased challenges as the number and variety of program sources, interrupt
sources, and configuration possibilities quickly multiply. Program audio can come from many sources, including
off-air receivers, two-way radios, telephone lines, satellite receivers, and cellular telephones. Interrupt audio (talent
cues) may be received with the program material connected via telephone lines or may need to come from the
mobile unit itself. The ability to provide IFB audio to a number of destinations is also required. These include
talent “belt pack” amplifiers, transmitters used with wireless receivers, and intercom systems.
A mobile IFB system must be easy to set up and quick to configure. It must be able to withstand the day in, day
out punishment of life “on the road.” Meeting these diverse requirements is made more difficult by the space
restrictions imposed by mobile facilities.
Studio Technologies has addressed these requirements with the IFB Plus Series products. The IFB Plus Series
consists of the Model 2 Central Controller, the Model 22 and model 24 Access Stations, the Model 32A and Model
33 Talent Amplifiers, and supporting accessories. These products combine the best features of studio IFB systems along with the special requirements of mobile applications. The end result is an IFB system that is flexible,
versatile, and extremely space efficient.
The heart of the IFB Plus Series is the Model 2 Central Controller. This one rack-space unit offers a wide range of
features all optimized for mobile applications. These include two independent IFB channels, an internal interrupt microphone, and four program inputs. Two telephone interfaces allow direct connection to telephone lines
or standard audio signals. The telephone interfaces can be used to receive and send IFB audio.
In addition to the Model 2’s internal interrupt microphone, up to four additional interrupt locations can be added
using Model 22 or Model 24 Access Stations. These additional locations allow producers, directors, or other
personnel to cue talent.
The Model 2 allows connection of up to four Model 32A or Model 33 Talent Amplifiers. Each is a compact, “belt
pack” unit whose output is compatible with all standard ear pieces and headsets. The Model 32A is a basic unit
intended for use by on-air personnel, while the Model 33 provides extra features that are useful for camera and
production personnel.
Model 2 Central Controller Front Panel
Issue 4, Page 1
A Feature-Packed Interruptible Foldback (IFB) System
Model 2 Central Controller
Two IFB Channels
The Model 2 contains two independent IFB channels. Each
channel has a complete set of controls and indicators. Program
source select switches allow one or more of the four program
inputs, as well as incoming audio from the two telephone interfaces, to be selected as program audio. Program level controls
allow adjustment of the selected program sources. Channel
audio level is displayed by 5-segment LED meters. Channel
interrupt activity is displayed by LED indicator lights.
Program Inputs
The Model 2 has four program inputs that can be individually
assigned to the two IFB channels. Each program input has
a trim pot that allows the nominal +4 dBu input level to be
adjusted over a ±8 dB ra nge. During interr upt activit y, prog ram
audio is muted. A sophisticated analog switch is used to give a
noise-free mute with absolutely no clicks or pops.
IFB Outputs
Each IFB output (program and interrupt audio) is sent to four
places: the talent amplifier output, a line output, telephone
interface 2, and the monitor amplifier. The talent amplifier
output provides IFB channel 1 and 2 audio, along with power
to support any combination of up to four Model 32A or Model
33 Talent Amplifier units. The balanced line-level output can
be used to drive wireless IFB transmitters, etc. Using telephone
interface 2, IFB audio from channel 1 or 2 can be used to originate an IFB feed. An external speaker or headphones can be
connected to the internal 4-watt amplifier, allowing monitoring
of either IFB channel.
Internal Interrupt Microphone
An electret-type microphone is contained behind the Model
2’s front panel. Two switches allow the internal microphone to
interrupt either IFB channel with clean, clear audio.
Telephone Interfaces
The Model 2 contains two telephone interfaces. Each interface
can be used to bring program or interrupt audio into the Model
2. In most applications, telco signals will be used as program audio sources. In special situations they can serve as an interrupt
source in conjunction with the voice operated (VOX) interrupt
function. The receive audio level of each telephone interface is
adjustable using a front panel control. In addition to receiving
audio, interface 2 can be used to originate an IFB feed. Using
this function, audio from IFB channel 1 or 2 can be sent to a
studio, a remote vehicle, or a portable telephone.
The telephone interfaces are unique in that they allow two
very different telephone “lines” to be correctly interfaced.
Each interface can be set to operate with a telephone line or
a standard audio signal. A telephone line would be a 2-wire
DC-biased circuit provided by a local telephone company.
A standard audio signal could be provided by, for example, a
cellular telephone.
The two operating modes supply distinct feature sets. When
an interface is set to the telephone line mode, full monitoring
and control is implemented. Each interface contains a switch
that allows the telephone line to be seized (taken off hook) or
hung up. When an interface is active, telephone line loop current is monitored. The interface will automatically hang up
if a telephone company provided disconnect signal is received.
Interface 2 also implements an auto answer function, “answering” the telephone line when ringing is detected.
When an interface is set to handle a standard audio signal, the
loop-current-specific features are disabled, and the interface
operates as a transformer-coupled balanced audio input. The
input and output audio levels are optimized for use with telephone-type audio signals.
Voice Operated (VOX) Interrupt
For special applications, the Model 2 allows an audio signal to
serve as both an interrupt audio source and a control source,
eliminating the need for a push-to-talk button or contact closure.
A switch is used to select the VOX audio source. The choices are:
receive audio from Telephone Interface 1, receive audio from
Telephone Interface 2, or audio from the VOX line-level input.
Monitor Amplifier
The Model 2 contains a 4-watt audio amplifier, allowing either
IFB channel to be monitored. A click-free analog switch mutes
the monitor output when the internal microphone is actively
interrupting an IFB channel. In addition, Model 22 or Model 24
Access Stations can be configured to mute the monitor amplifier upon interrupt.
Audio Quality
Great care was taken to make the Model 2’s audio sound clear
and crisp. The unit’s specifications belie its seemingly humble
function as an IFB unit. This unit sounds great!
Model 2 Central Controller Back Panel
Studio Technologies, Inc. IFB Plus Series, Issue 4, Page 2
Each IFB channel includes a studio-quality compressor circuit.
The compressors even out variations in interrupt audio signals,
smoothly controlling pea k sig nal levels. They make t alent cues
more intelligible and help reduce the risk of abnormally high
signal levels from reaching the talent’s ears.
line-level audio source can be connected. Up to four Model 24
units can be connected and supported by two Model 2 units. The
Model 27A 19-Inch Rack Adapter allows a Model 24 and a Model
11A Gooseneck Microphone to be mounted in a single space of a
standard rack enclosure.
Installation
For easy installation and maintenance, standard connectors
are used throughout, including male and female XLR-type,
¼-inch tip and sleeve, 9-pin D-subminiature, and modular
telephone jacks. Mains power is factory selected for 115 or 230
V, 50/60 Hz. The Model 2 is mounted in one space of a standard
19-inch rack.
Model 22 Access Station
While the Model 2 can be used completely “stand-alone,”
the Model 22 Access Station can be used to provide additional
IFB origination locations. The access stations are installed at
pos itions convenie nt to producer s, d irectors, or others who ne ed
to cue talent and related personnel. As many as four Model 22
can be used with each Model 2 Central Controller.
The Model 22 consists of a metal chassis containing two lighted
pushbutton switches, microphone and line inputs, and status
and control circuitry.
The mic input is configured for the connection of an electret gooseneck microphone. The line input, compatible with
balanced and unbalanced signals, allows another piece of
communications equipment to provide interrupt audio. This
allows direct interfacing with intercom systems from companies
such as Telex®/RTS® and Clear-Com®.
Several mounting options are available. One adapter allows the
Model 22 to be mounted in a single rack space. A second adapter
is used to install the Model 22 in a table or console opening.
Model 32A & Model 33 Talent Amplifiers
The Model 32A and Model 33 Talent Amplifiers are self-contained
“belt pack” units that drive talent ear pieces or headsets. A single
3-conductor microphone-type cable links the Model 2 with the talent amplifiers. Each Model 32A and Model 33 contains both a male
and female XLR-type connector, allowing simple “loop through”
connection of multiple units. Up to four talent amplifiers can be
connected to, and powered by, a single Model 2 Central Controller. On each talent amplifier the audio output signal is provided
on a standard ¼-inch phone jack. An LED on each unit lights
whenever power is present, providing setup assistance and user
confidence. Identical in size, each is housed in a lightweight, yet
rugged, aluminum housing that includes a belt clip. An optional
mounting adapter is available, allowing a Model 32A or 33 to be
installed in a permanent location.
The Model 32A is intended for use by on-air personnel, and contains a source switch, along with an output level control. Either
IFB channel 1 or IFB channel 2 can be sent to the talent, along with
the desired audio “volume.” For user convenience, both ¼-inch
and 3.5 mm output jacks are provided.
The Model 33 is unique in that a “mix” of IFB channels 1 and 2 can
be created. Two level controls, along with a source select switch,
allows camera and production personnel to hear IFB cues from
either or both channels. This allows IFB signals intended for both
technician and talent to be simultaneously monitored.
Model 24 Access Station
The Model 24 Access Station allows broadcast personnel to
access four IFB channels associated with two Model 2 units.
The unit contains five lighted pushbutton switches, four of
which are used to activate and display the status of the IFB
channels and one that provides an “all call” function. The
Studio Technologies Model 11A Gooseneck Microphone or a
Model 22 Access Station (shown with
optional Model 25A Rack Adapter and
Model 11A Gooseneck Microphone)
Model 24 Access Station (shown with
optional Model 27A Rack Adapter and
Model 11A Gooseneck Microphone)
Studio Technologies, Inc. IFB Plus Series, Issue 4, Page 3
Model 32A Talent Amplifier (top)
Model 33 Talent Amplifier (bottom)
IFB Plus Specifications
Model 2 Central Controller
IFB Channels: 2
Channel Features: 6-input program select switch, program level
control, 2 status LEDs, 5-segment LED level meter
General Audio Parameters:
Audio Switching and Muting: “clickless” using special “ramping”
analog switches
Distortion (THD+N): 0.3%
Overall Frequency Response: 20 Hz to 20 kHz, ±0.5 dB
S/N Ratio: 67 dB
Interrupt Audio Compressor/Limiters: one per IFB channel, studio
quality, dual slope
Connectors:
Audio Inputs: 3-pin XLR-type, female
Audio Outputs: 3-pin XLR-type, male
Talent Amplifier Output: 3-pin XLR-type, male
Monitor Amplifier Output: ¼-inch, 2-conductor phone jack
Access Station: 9-pin, D-subminiature, female
Tele ph o ne I nte r f a c e s : 6-position modular (RJ11-type jack)
Mains Power: standard 3-blade IEC-type plug
Internal Interrupt Microphone: electret condenser
Program Inputs: 4
Ty pe : electronically balanced, direct coupled
Impedance: 24 k ohms
Level: +4 dBu, nominal, trim adjustable ±8 dB
Auxiliary Audio Input:
Ty pe : electronically balanced, direct coupled
Impedance: 24 k ohms
Level: +4 dBu, nominal, trim adjustable ±8 dB
Application: used with voice operated (VOX) interrupt
Talent Amplifier Output:
Application: provides power and audio signals for up to four
Model 32A or Model 33 Talent Amplifiers. The output connector
(3-pin XLR-type, male) has common on pin 1, +22 Vdc modulated
with channel 1 audio (nominal –10 dBu) on pin 2, and channel 2 audio
(nominal –10 dBu) on pin 3.
Line Outputs: 2, 1 per IFB channel
Ty pe : electronically balanced, capacitor coupled, intended to drive
600 ohm or greater loads
Level: +4 dBu, nominal, +24 dBu maximum
Voice Operated (VOX) Interrupt Function:
Input Source: receive audio from telephone interface 1 or 2, or
auxiliary audio input, selectable
Output: IFB channel 1 or 2, selectable
Detection Bandpass: 400 to 1400 Hz, nominal
Detect Time: less than 1 mSec
Telephone Interfaces 1 and 2:
Operating Modes: switch selectable for use with telephone lines or
standard balanced or unbalanced audio signals
Receive Audio Level: –15 dBu, nominal, trim adjustable ±8 dB
Telephone Line Requirements: 2-wire, loop start, 10 mA loop
current minimum
Telephone Line Disconnect: manual, using front-panel switch; automatic, after detection of 250 mSec, nominal, break in loop current
Telephone Line Interface Control: switch on front panel allows
manual off-hook and manual hang-up functions
Telephone Interface 2—Additional Features:
Auto Answer: when set for telephone line operation, answers on
one ring
Audio Routing Control: switch on front panel allows Interface 2 to
receive audio, or send IFB channel 1 or 2 audio
Send Audio Level: –6 dBu, nominal
Monitor Output:
4 W RMS into 8 ohms @ 1% THD+Noise
Power:
Application: designed to drive loads of 8 ohms or greater
Access Station Interface: allows connection of up to four Model 22
or Model 24 Access Stations
AC Mains Requirement: 115 or 230 V, ±10%, internally configurable,
50/60 Hz, 20 watts maximum
Dimensions (Overall):
19.00 inches wide (48.3 cm)
1.72 inches high (4.4 cm)
11.4 inches deep (29.0 cm)
Mounting: one space in a standard 19-inch rack
Weight: 10.4 pounds (4.7 kg)
Model 22 Access Station
Mounting: rack mounted using Model 25A 19-inch Rack Adapter.
Panel mounted using Model 28A Panel Adapter; custom mounting
easily accomplished.
Interconnection: two 9-pin D-subminiature connectors (female),
one intended to link Model 22 to Model 2 Central Controller, the
second designed to allow “loop through” installation for connection
to additional Model 22(s)
Interrupt Switches: 2
Ty pe : back lit, momentary, EAO 99-series
Tac t i le S ensat ion: excellent!
Audio Input: electret microphone or line level, switch selectable
Microphone Input:
Compatibility: designed for use with Studio Technologies’
Model 11A Gooseneck Microphone
Connector: three terminals on a screw terminal strip
Line Input:
Ty pe : electronically balanced, capacitor coupled, compatible with
balanced or unbalanced audio signals
Input Impedance: 24 k ohms
Input Level: –15 to +10 dBu, adjustable via trim potentiometer
Connector: two terminals on a screw terminal strip
Monitor Muting: switch selectable, allows Model 22 interrupt
activity to mute monitor amplifier on Model 2 Central Controller
Power Requirements: +18 Vdc filtered and regulated, 25 mA
maximum, provided by Model 2 Central Controller
Dimensions (Overall):
6.4 inches wide (16.3 cm)
21.6 inches high (4.1 cm)
5.2 inches deep (13.2 cm)
Weight: 0.8 pounds (0.35 kg)
Studio Technologies, Inc. IFB Plus Series, Issue 4, Page 4
Model 22 Access Station
Mounting: rack mounted using Model 27A 19-inch Rack Adapter
(purchased separately); can also be flush mounted in customfabricated rectangular opening in enclosure or work surface
Interconnections: two 9-pin D-subminiature connectors (female),
each linking the Model 24 with a Model 2 Central Controller
Interrupt Switches: 5
Functions: IFB 1-4, All Call
Ty pe : momentary pushbutton, EAO 99-series, all backlit, tally
indication for IFB 1-4 functions
Microphone Input:
Compatibility: 2-wire electret, designed for use with Studio Tech-
nologies’ Model 11A gooseneck microphone (purchased separately)
Connector: three terminals on a screw terminal strip
Line Input:
Ty pe : transformer coupled, compatible with balanced or unbalanced
audio signals
Input Impedance: 40 k ohms, nominal
Input Level: –15 to +10 dBu, adjustable using trim potentiometer
Connector: two terminals on a screw terminal strip
Monitor Muting: switch selectable, allows Model 24 interrupt activity
to mute monitor amplifier outputs on Model 2 Central Controllers
Power Requirements: +18 volts DC, 50 milliamperes, nominal,
provided by connected Model 2 Central Controllers
Dimensions (Overall):
6.40 inches wide (16.3 cm)
21.60 inches high (4.1 cm)
5.20 inches deep (13.2 cm)
Weight: 0.8 pounds (0.35 kg)
Model 32A Talent Amplifier
Application: intended for portable applications. Contains integral belt
clip. Optional adapter available to allow permanent mounting.
Indicator Light: 1, indicates presence of operating power
Input Connector: 3-pin XLR-type, female
Loop Through Connector:
Ty pe : 3-pin XLR-type, male. Connected in parallel with input
connector. Intended to be used to connect multiple talent amplifiers
in a “loop through” arrangement.
Audio Source: IFB channel 1 or channel 2, switch selectable by user
Audio Output:
Connectors: ¼-inch and 3.5 mm, 2-conductor (monaural) phone jacks
Load: intended for connection to headphones or earpieces with
impedance of 8 ohms or greater
Output Level: user adjustable via potentiometer
Maximum Output Power: 170 mW into 8 ohms at 1% THD+Noise,
400 Hz
Distortion: <0.15%, THD+Noise, measured at 400 Hz with 100 mW
output power into 8 ohms
Frequency Response: optimized for voice response (100 Hz to
20 kHz, ±0.5 dB)
Dimensions (Overall):
3.25 inches wide (8.3 cm)
1.80 inches high (4.6 cm)
3.95 inches deep (10.0 cm)
Weight: 0.6 pounds (0.3 kg)
Model 33 Talent Amplifier
Application: intended for portable applications. Contains integral belt
clip. Optional adapter available to allow permanent mounting.
Indicator Light: 1, indicates presence of operating power
Input Connector: 3-pin XLR-type, female
Loop Through Connector:
Ty pe : 3-pin XLR-type, male. Connected in parallel with input
connector. Intended to be used to connect multiple talent amplifiers
in a “loop through” arrangement.
Audio Source: IFB channel 1 and/or channel 2, switch selectable by
user
Audio Output:
Connector: ¼-inch, 2-conductor (monaural) phone jack
Load: intended for connection to headphones or ear pieces with
impedance of 150 ohms or greater
Output Level: user adjustable via potentiometer
Maximum Output Power: 35 mW into 150 ohms @ 1% THD+Noise,
400 Hz
Distortion: <0.15%, THD+Noise, measured at 400 Hz with 32 mW
output power into 150 ohms
Frequency Response: optimized for voice response (100 Hz to
20 kHz, ±0.5 dB)
Dimensions (Overall):
3.25 inches wide (8.3 cm)
3.95 inches high (10.0 cm)
1.8 inches deep (4.6 cm)
Weight: 0.6 pounds (0.3 kg)
Features and specifications subject to change without notice.
Studio Technologies, Inc.
5520 West Touhy Avenue
Skokie, Illinois 60077 USA
Telephone 8 47- 676-917 7
Fax 847-982-0747
www.studio-tech.com
© by Studio Technologies, Inc., February 2007
50136-0207, Issue 4
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